Organics

Chiral mono- and bis-(thio)urea supramolecular organocatalysts were studied in the enantioselective vinylogous addition reaction of 2-trimethylsilyloxyfuran (TMSOF) to carbonylic compounds; the corresponding chiral γ-hydroxymethyl-butenolides are obtained in good yields and with high enantiomeric excesses. The catalyst structure, as well as the reaction conditions, strongly influence the efficiency of the reaction. The conformational features of mono(thio)urea catalysts 2 and 3 and bis(thio)urea catalysts 7 and 8 were investigated by DFT calculations along with the structure of their complexes with benzaldehyde. Natural Bond Orbital (NBO) and Non-Covalent Interaction (NCI) calculations provided useful information concerning the activating H-bonding interactions in the complexes. Full article

A series of fourteen O-ethyl-N-butylphenylphosphonamidates with benzyl ether substituents at the ortho position was prepared and fully characterised. Upon treatment with n-butyllithium in THF at RT, they underwent cyclisation in eight cases to give the novel 2,3-dihydrobenzo[d][1,3]oxaphospholes in moderate to low yield as a single diastereomer, for which the relative configuration was determined by X-ray diffraction in one case. Full article

The chloro-P,N-{diphenylphosphanyl-[(5-phenyl-1,3,4-oxadiazol-2-ylamino)phenyl-me- thyl]}(p-cymene)ruthenium(II) hexafluorophosphate complex (4) was obtained in two steps from diphenylphosphanyl-[(5-phenyl-1,3,4-oxadiazol-2-ylamino)phenyl-methyl] borane (2). In the first step, the oxadiazole ring coordinated with the ruthenium atom, resulting in the formation of the dichloro-N-{diphenylphosphanyl-[(5-phenyl-1,3,4-oxadiazol-2-ylamino)phenyl-methyl]borane}(p-cymene) ruthenium(II) complex (3). During the crystallization of the P,N-chelate ruthenium complex, the formation of conglomerate crystals was revealed by X-ray structure analysis. Only two stereoisomers were obtained with (S)-Ru and (R)-C configurations in the first complex and with (R)-Ru and (S)-C configurations in the second. This deracemization during crystallization is due to the formation of a hydrogen bond between the P,N-ligand and the chlorine atom (CH•••Cl). This supramolecular interaction allows the transfer of the ligand chirality to the metal center and decrees the stereochemistry of the ruthenium atom. Full article

4-Hydroxy-2-pyrones are of interest as potential biorenewable molecules for a sustainable transition from biomass feedstock to valuable chemical products. This review focuses on the methodologies for the synthesis of 4-hydroxy-2-pyrones published over the last 20 years. These pyrones as polyketides are widespread in Nature and possess versatile bioactivity that makes them an attractive target for synthesis and modification. Biosynthetic paths of the pyrones are actively developed and used as biotechnological approaches for the construction of natural and unnatural polysubstituted 4-hydroxy-2-pyrones. The major synthetical methods are biomimetic and are based on the cyclization of tricarbonyl compounds. Novel chemical methods of de novo synthesis based on alkyne cyclizations using transition metal complexes and ketene transformations allow for straightforward access to 4-hydroxy-2-pyrones and have been applied for the construction of natural products. Possible directions for further pyrone ring modification are discussed. Full article

The modern trend in sunscreen products is towards the development of UV filters with multi-functional properties, to provide a broad shielding against ultraviolet radiation, antioxidant activity, and the prevention of skin cancer. Additionally, they should also be safe for humans as well as the environment. The benzimidazole heterocycle is a suitable platform for the development of such multifunctional molecules with potential application in cosmetic formulations, due to their ability to act as both UV protectors and reactive pharmacophores. This review presents for the first time the progress in the synthesis and optimization of benzimidazole compounds as UV sunscreen filters. The modifications to the substitution pattern of the lead compound and structure–activity relationships are discussed, as well as the synthetic approaches for the preparation of 2-substituted benzimidazoles. These aggregated data will be useful in future in the development of modern benzimidazole-based sunscreen. Full article

Mannich bases are a class of organic compounds usually obtained by the condensation reaction between an amine, a compound with active hydrogens, and an aldehyde. They are versatile intermediates in organic synthesis, and those compounds containing this motif find applications in pharmaceutical, agrochemical, and even material fields since they are widely known for their wide range of biological activities, including antimicrobial properties. Thus, as part of our interest in antifungal agents, this narrative review aimed to gather information from the literature on the synthesis of various representative Mannich-base-containing compounds, particularly centered on those exhibiting antifungal properties. In this context, the compilation indicated that Mannich bases could be considered as a relevant toxophore/pharmacophore by incorporating heterocyclic moieties to be implemented for the design of new antifungal agents, given its proven efficacy against phytopathogens, other opportunistic human pathogens, and some dermatophytic fungal species, which can be further exploited as agrochemical agents or in medicinal applications to treat fungal infections. The antifungal effect exhibited by Mannich bases conjugated with oxa and/or aza-heterocycles suggests that compounds that have a heterocyclic system attached to the β-amino core are attractive alternatives oriented to the synthesis of novel and helpful antifungal agents. Full article

The origin of individual features in the ground state absorption spectra of two protonated corroles differing in the architecture of peripheral substitution (either C_m-aryl or C_b-alkyl) have been studied in detail with the ground state absorption spectroscopy and density functional theory calculations. The geometry optimization, molecular orbitals and absorption spectra calculation have been carried out. It was found that protonation leads to the saddle type macrocycle conformation in contrast with the wave type conformation known for the parent-free base corroles. The mean plane deviation parameter Δ23 for the macrocycle, pyrrole tilting angles and the degree of pyramidalization λ² of all four pyrrole nitrogens was found to depend on the peripheral substitution architecture. Macrocycle conformation of the protonated forms has distinct asymmetrical features which are reflected by the sets of values of the tilting angles and values of pyramidalization degree. The pair of pyrroles B and C has smaller tilting angles and higher pyramidalization degree values, whereas the opposite trend was found for the pair of pyrroles A and D. Electronic effects and structural differences induced by substitution lead to the pronounced shifts of the molecular orbitals. In the C_b-alkylated corrole, almost-degenerated HOMO and HOMO-1 molecular orbitals lead to enhancement of the configuration interaction. As a result, the Q_x transition oscillator strength goes down, becoming comparable to that of the Q_y one. A large HOMO-HUMO-1gap in the C_m-aryl corrole minimizes the configuration interaction, giving rise to Q_x band domination in the visible range spectrum. Full article

Alkoxy radicals have been identified as versatile intermediates in synthetic chemistry in the last few decades. Over the last decade, various catalytic processes for the in situ generation of alkoxy radicals have been explored, leading to the development of new synthetic methodologies based on alkoxy radicals. In this review, we provided a comprehensive review of recent developments in the utilization of alkoxy radicals in diverse organic transformations, natural product synthesis, and the late-stage modification of bioactive molecules through the implementation of the photoredox methodology. Full article

In the present work, we report a thermoresponsive hydrogel formed by the self-assembly of compounds 1 and 2 Milli Q water. Both hydrogels showed thixotropic behavior. Atomic force microscopy (AFM) studies confirm the fiber-like microstructure of compounds 1 and 2, but denser fibers were observed in the case of compound 1. The hydrogel formed by compound 1 detected Cu²⁺, Fe³⁺, and Hg²⁺, whereas the hydrogel of 2 showed a change in the optical signal, specifically upon adding Cu²⁺ and Hg²⁺. Mechanistically, adding metal ions to the hydrogel resulted in the formation of a (1:1) complex with Fe³⁺ and Hg²⁺ and (2:1) with Cu²⁺. The detection of metal ions has also been achieved in real-life samples, such as in tap water. Low-cost portable gel-coated paper strips have also been developed for the onsite detection of these metal ions. Full article

Triazolo[4,3-a]pyrimidine is one of the promising structural fragments for the development of drugs, including anticancer drugs. This work is devoted to the synthesis of a number of new 2-arylhydrazone derivatives of thiazolo[3,2-a]pyrimidine, which are synthetic precursors for triazolo[4,3-a]pyrimidines. The crystal structure of 6-acetyl-7-methyl-5-phenyl-2-(2-phenylhydrazineylidene)-5H-thiazolo[3,2-a]pyrimidin-3(2H)-one was established by SCXRD. In the reduction reaction of the compound, the following system was used: vanadium(V) oxide, and sodium borohydride in ethanol at room temperature, which led to the formation of only one pair of diastereomers (1R*)-1-((5S*,6R*,7R*)-(1-(hydroxymethyl)-7-methyl-1,5-diphenyl-1,5,6,7-tetrahydro[1,2,4]triazolo[4,3-a]pyrimidin-6-yl)ethan-1-ol. Full article

This review presents all currently known macroheterocyclic compounds that include a bispidine (3,7-diazabicyclo[3.3.1]nonane) fragment in their structure. A classification of bispidine-containing macroheterocycles, which is based on the ring size and the nature of bispidinic nitrogen atoms, is suggested. Synthetic approaches to the studied compounds are classified and considered. The features of the crystal structures and solution behavior of bispidine macroheterocycles are analyzed. Prospects for the development of these organic receptors are proposed. Full article

Cyclometallated iridium(III) and platinum(II) complexes are intensely used in optoelectronics for their photophysical properties and ability to convert excitons from singlet to triplet state, thus improving the device efficiency. In this contribution, we report the multi-steps synthesis of an electrodeficient dipyridylbenzene-like terdentate ligand [N^C^N], namely 2′,6′-dimethyl-2,3′:5′,2″-terpyridine (6), with 18% overall yield. Compound 6 has been employed to synthesize two phosphorescent complexes of platinum(II) and iridium(III), namely compounds 7 and 8, respectively. Both complexes have been characterized by NMR and high resolution mass spectrometry, and demonstrate high luminescence quantum yields in a deaerated solution at room temperature, with 18% and 61% for 7 and 8, respectively. If the iridium(III) complex displays similar emission properties to [Ir(dpyx)(ppy)Cl] (dpyx = 3,5-dimethyl-2,6-dipyridylbenzene and ppy = 2- phenylpyridine), the platinum(II) derivative, with λ_em = 470 nm, is a rare example of a fluorine atom-free blue emitting [N^C^N]PtCl complex. Full article

The thermal degradation and flammability characteristics of some common fibre-forming polymers, such as polypropylene (PP) and polyacrylonitrile (PAN), are described in this review paper. The flame retardance of these polymers is principally affected by reactive routes that were primarily developed in our laboratories. The modifying groups that are incorporated into polymeric chains include phosphorus- or phosphorus/nitrogen-containing moieties in different chemical environments. The degradation characteristics and extent of flame retardance were mainly evaluated using routine thermal and calorimetric techniques. Elements of flame-retardant mechanisms occurring in the condensed and vapour phases were also identified. Furthermore, we also explored the effects of molecularly dispersed β-cyclodextrin, including its physical mixtures, on the thermal and combustion characteristics of PAN. Given that both types of polymers are often used in the form of fibres, and that the aspect ratio of fibrous materials is relatively high, even nominal enhancements in their fire retardance are highly welcomed. Hence, the preliminary results of our research on chemically modified PAN incorporating molecularly dispersed β-cyclodextrin are encouraging in terms of their enhanced fire retardance, and hence this field warrants further exploration. Full article

New methyl-substituted, and diphenyl-substituted fused dipyranoquinolinones are prepared in excellent yields via the triple bond activation and 6-endo-dig cyclization of propargyloxycoumarin derivatives by gold nanoparticles supported on TiO₂ in chlorobenzene under microwave irradiation. In the absence of gold nanoparticles, the methyl-substituted propargyloxycoumarin derivatives resulted in fused furopyranoquinolinones through Claisen rearrangement and 5-exo-dig cyclization. The intermediate propargyloxy-fused pyridocoumarins are prepared by propargylation of the corresponding hydroxy-fused pyridocoumarins. The methyl-substituted derivatives of the latter are synthesized in excellent yield by the three-component reaction of amino hydroxycoumarin with n-butyl vinyl ether under iodine catalysis. The diphenyl-substituted derivatives of hydroxy-fused pyridocoumarins are obtained, also, by the three-component reaction of amino hydroxycoumarin with benzaldehyde and phenyl acetylene catalyzed by iron (III) chloride. Preliminary biological tests of the title compounds indicated lipoxygenase (LOX) (EC 1.13.11.12) inhibitory activity (60–100 μM), whereas compound 28a, with IC₅₀ = 10 μM, was found to be a potent LOX inhibitor and a possible lead compound. Only compounds 10b and 28b significantly inhibited lipid peroxidation. Full article

This review is dedicated to the different varieties of macrocycles synthesis bearing indole units in their architecture by metal-catalyzed strategies. The progress of the new macrocyclization approaches is persisted be a keen area of research. Macrocycles contain a wide variety of molecules, and among those, heteroaryl motifs are valuable constituents that provide an attractive feature to macrocyclic systems. Indole represents one of the privileged pharmacophores against a variety of targets with various biological applications. Among the nitrogen-based heterocycles, indole plays a prominent role in organic synthesis, medicinal chemistry, pharmaceuticals, natural products synthesis, agrochemicals, dye and fragrances, and drug design. These scaffolds are widely distributed in several bioactive natural products and synthetic macrocycles constructed against a specific biochemical target and the most common constituents of naturally occurring molecules. Due to its immense importance, the progress of novel approaches for the synthesis of indole-based scaffolds has increased steadily. The majority of the macrocycles synthesis proceeds through the macrolactamization and macrolactonization, as well as the C–C bond macrocyclization process described by metal-catalyzed ring-closing metathesis (RCM) and coupling reactions. Among macrocyclizations, metal-catalyzed approaches are considered one of the most powerful tools for synthetic chemists in the design of a variety of macrocycles. This review aims to give a comprehensive insight into the synthesis of varieties of macrocycles bearing indole scaffold catalyzed by various transition metals that emerged in the literature over the last two decades. We hope that this review will persuade synthetic chemists to search for novel strategies for the C–C bond macrocyclization by metal-catalyzed protocols. Full article

Starting from acid chlorides, alkynes, tryptamines, and acryloyl chloride, 21 densely substituted tetrahydro-β-carbolines were prepared in a four-component, one-pot reaction. In this study, the aza-Michael addition step to generate intermediate enaminones was optimized in the presence of ytterbium triflate. Moreover, apart from acryloyl chloride, all reactants could be deployed in almost equimolar ratios, which increases the atom economy of the sequence. For mechanistic rationalization, the concluding aza-anellation was investigated by DFT calculations on potential intermediates and corresponding activation energies, revealing that the aza-anellation proceeds via ene reaction rather than via electrocyclization. Full article

Formaldehyde is a simple chemical compound that is used as a building block in obtaining a wide range of products. The versatility of formaldehyde in chemical synthesis becomes evident when it is reacted with N-alkylethylenediamines. Therefore, this paper reports the structure and reactivity of a series of compounds derived from easily accessible molecules, such as formaldehyde, sodium hydrosulphide, and N-alkylethylenediamines. The 1,3,5-triazines (1a-1d) and bis(3-alkyl-imidazolidin-1-yl)methanes (2a-2d) were obtained by simple reaction conditions. Additionally, different proportions of sodium hydrosulphide and formaldehyde were used with N-benzylamine to obtain N-benzyltriazinane (3), N-benzylthiadiazinane (4) and N-benzyldithiazinane (5). All these compounds were characterized by analytical, spectroscopic, and spectrometric techniques, such as melting point, solubility, one-dimensional and two-dimensional nuclear magnetic resonance (¹³C, ¹H, ¹⁵N, COSY, HETCOR, NOESY, COLOC), elemental analysis, high- and low-resolution mass spectrometry, among others. The structures of compounds 4 and 5 were obtained by single-crystal X-ray diffraction. The results show that small variations in the stoichiometry and the reaction conditions significantly influence the products obtained. Full article

The activation of C-H bonds is a potent tool for modifying molecular structures in chemistry. This article details the steps involved in a novel ligand bearing a bicyclic [3.3.1]-nonane framework and bissulfoxide moiety. A palladium catalyzed allylic C-H oxidation method enables a direct benzyl-allylic functionalization with the bissulfoxide ligand. Bissulfoixde ligand possesses a rapidly constructed bicyclic [3.3.1] framework and it proved to be effective for enabling both N- and C-alkylation. A total of 13 C-H activation productions were reported with good to excellent yields. This report validated that it is necessary to include bissulfoxide as a ligand for superior reactivities. Naftifine was produced utilizing developed C-H functionalization methodology in good overall yields. Full article

Great efforts of the scientific community are focused on the development of catalysts for the reduction of carbon dioxide (CO₂) to useful molecules such as carbon monoxide, formic acid, methanol, ethanol, methane, ethylene, or acetate. Various metal porphyrin complexes were synthesized and studied to develop highly active and selective catalysts. While the substituents on the porphyrin core (the primary coordination sphere) determine the reactivity of the metal, the introduction of the secondary coordination is important for the binding and activation of CO₂. In this review, selected examples of iron porphyrin catalysts with a secondary coordination sphere capable of stabilizing intermediates of the CO₂ reduction process by hydrogen bonding are presented. Full article